This invention relates to a method for determining the 3D coordinates of an object and to an apparatus for carrying out such method.
In the method, a pattern is projected onto the object. The light reflected by the object is captured and evaluated. The apparatus for carrying out such method comprises a projector for projecting a pattern onto the object, a camera for recording the object, and an evaluating means for evaluating the shots recorded.
Methods and apparatuses of this kind are known already, for example from DE 10 2006 048 234 A1 and DE 10 2007 042 963 A1. In these methods, a stripe pattern can be projected onto the object. Usually, the stripe pattern is projected onto the object by the method of white-light stripe projection, i.e. with white light.
As for determining the 3D coordinates of the object a single shot generally is not sufficient to satisfy the measurement requirements and/or to completely cover the object, it is required to position the pattern projection system at various recording positions in the space and to transfer the shots made there into a common, superordinate coordinate system, which can also be referred to as absolute coordinate system. This process frequently referred to as “global registration” requires a high accuracy.
In a previously known method of this kind shots are made which partly overlap. These shots can be oriented to each other via an optimization of the overlap regions. However, with larger objects with little surface structure, the method possibly is not sufficiently accurate.
Furthermore, there are known methods in which reference marks are used, which are mounted on and/or beside the object and/or on one or more of the set-ups surrounding the object. The reference marks initially are calibrated. Preferably, this is effected by the method of photogrammetry. By means of the reference marks, which are detected by a pattern projection system, in particular a stripe projection system, the various shots of the object can be transformed onto the calibrated points, so that a global registration is possible.
From EP 2 273 229 A1 a method is known, in which for determining the 3D coordinates of an object a stripe pattern is projected onto the object by a projector. The stripe pattern reflected by the object is recorded by a camera which comprises an optical system and an area sensor, in particular a CCD sensor or CMOS sensor. The projector and the camera form a stripe projection system. In the vicinity of the object a plurality of reference set-ups are arranged, which each include a plurality of reference marks. The reference set-ups initially are surveyed. Subsequently, the 3D coordinates of the object are determined by the stripe projection system.
From WO 2004/011876 A1 an apparatus according to the generic part of claim 8 is known. The apparatus comprises a projector for projecting a pattern onto the object, a camera for recording the object, and an evaluating means for evaluating the shots of the object. The apparatus furthermore comprises a projection means for projecting reference marks onto the object and a further camera for recording the reference marks.
From DE 195 36 297 A1 a method for the geometrical calibration of optical 3D sensors for the three-dimensional survey of objects is known, in which a pattern is projected onto the object and the light reflected by the object is recorded and evaluated by a camera. In the image field of the camera a calibration means with at least four calibrated and a plurality of further signal marks or reference marks is located, which are recorded by the camera.
From DE 10 2005 051 020 A1 a method for the three-dimensional digitization of bodies is known, in which a camera is moved around the body to be digitized. The body to be digitized is surrounded by a plurality of photogrammetrically evaluable marks. Around the body, a plurality of light pattern projectors furthermore are stationarily mounted, which are switched on one after the other.
US 2010/0092041 A1 discloses a method for determining the three-dimensional shape of an object, in which a pattern is projected onto the object and the light reflected by the object is captured and evaluated by a camera. The camera furthermore detects a reference mark beside the object.